Radiation pattern identifying apparatus



April 19, 1960 T. I. RESS RADIATION PATTERN IDENTIFYING APPARATUS Filed Jan. 10, 1956 INVENTOR THOMAS l. RESS ATTORNEYS United States Patent RADIATION PATTERN IDENTIFYING APPARATUS Application January 10, 1956, Serial No. 558,288

8 Claims. (Cl.-250 83.6)

-This invention relates generally to ion discharge apparatus wherein the discharges are initiated by electro- 7 2,933,610 .Paterrted Apr. 19, 196i) means. Itjwill be appreciated that the number of sensing electrodes can be increased as desired, and the mutual spacing between sensing electrodes be conversely decreased as' desired to increase the accuracy with which the shape of the plasma pattern can be determined.

For a better understanding of the invention, reference is made to the following description of an exemplary embodiment of the invention, the description to betaken with the accompanying drawings wherein: p Fig. 1 is a front view of an embodiment accordingito the invention; f Fig. 2 is a view of the said embodiment taken in cross I section as indicated by the arrows 2-2. in Fig. 1;

magnetic radiations, as, say, X-rays, ultraviolet rays, visible light, or infrared rays. More particularly, this invention relates to ion discharge apparatus of this character wherein an input pattern of radiation to the apparatus causes ionization therein in a localized plasma region whose configuration reproduces the pattern of the radiation received by the apparatus.

It is an object of the invention to provide apparatus capable of selectively identifying or recognizing a large number of difi'erent radiation patterns received by the apparatus.

It is another obiect of the invention to provide apparatus or" the abovenoted character wherein the dif ferent radiation patterns are distinctively indicated'by diferent combinations of electrical indications.

These and otherobjects are realized according to the invention by providing apparatus comprising-a first electrode of sizable extent in two coordinates of a three coordinate system for measuring space, a second electrode coextensive with the first electrode in the named two coordinates and spaced from the first electrode in the direction of the third coordinate, and a closure means which maintains an ionizable medium in the space between the two electrodes. The first electrode is pervious to ionizing radiation of the sort described above. A voltage source is coupled betwen the first electrode and the second electrode to render the intervening medium ionizabie by radiation which penetrates the first electrode. The spacing betw en the electrodes, the nature of the ionizable medium, and the value of voltage applied across the electrodes are such that a pattern of radiation penetrating the first electrode will ionize the medium only in alocalized plasma region whose pattern duplicates thepattern of the incoming radiation.

To determine the configuration of the localizedplasma region, there is provided a plurality of at least v three sensing electrodes disposed in the medium at points which are distributively spaced in thefirst-mentioned two coordinates to form a network-of plasma sensing points.

Anelectric energy source energizes all of the sensing electrodes at a voltage lower than the ionizing voltage for the medium. Since a plasma region is a low impedance region, the electric energy source will. cause current to flow through the ones of the sensing electrodes in contact with the plasma in a plasma pattern formed in the medium by the received radiation pattern. The current flow through? sensing electrodes having no contact with the plasma of, the plasma'pattern will be negligible at the best inasmuch as a very high impedance to current flow is offered by the medium outside of the plasma pattern. Since the locations-of all the sensing electrodes are known, it is only necessary to determine rent flow is-made by suitable current responsive indicator Fig. 3 is an enlarged view in cross section of aportion of the view in Fig. 2; and I Fig. 4 is a schematic diagram of certain .of the electrical connections of the said embodiment.

Referring 'now to Figs. 1 and 2, the number 10 designates a glass plate whose left-hand face, as seen in Fig. 2, is rendered electroconductive by depositing a coating 11 of an electroconductive material (as, say, zinc oxide) on the face, and by then fusing the coating 11 into the glass It). The plate 10 and coating 11 together represent the mentioned first electrode which is perviousto ioniz ing radiation. The presently-described embodiment is adapted to identify radiation patterns formed by visible light, and, to this end, both the glass plate 10 and the coating 11 are light transparent.

Disposed in spacedpar'allel relation from the plate 10 is an insulating plate 15 having depositedon the face thereof towards plate ll) a coating 16 of high impedance electroccnductive material, as, say, carbon; This, coating 16 represents the mentioned second electrode. The plate 15 is penetrated by a plurality of low impedance (eig'. metallic) rod electrodes 17a, 17b, 17c, 17d and 17e (Fig. 1). As shown, the rod electrode 17a occupies a central position, and the rod electrodes 17b-17e are symmetrically disposed about the electrode 17a. Each of the rod electrodm extends through and beyond the insulating'plate member 15 towards the glass plate 10. Preferably, the electrodes 17a-17e extend towardsplate 10 no futher than to be in flush relation withthe outer surface of the high impedance electroconductive coating 16. As best shown in "Fig. 3, voids are left in the coating 16 in localized areas thereof which respectively surround the rod electrodes. V

The plates 10 and 15 are held in spaced apart relation by a gasket 20 which encircles the respective periphcries of the plates. The gasket 20 additionally acts as' a closure means to maintain an ionizable medium 21 in Y the space between the plates 10 and 11. The medium 21 may consist, for example, of a mixture of nitrogen and argon reinforcedby a small percentage'of a gaseous quenching compound such as ether vapor .or vapors of suitable alcohols. The ionizable medium 21 may be hermetically sealed in the space between the. plates 10 and 15 by the gasket 20. For better operation of the apparatus, it is preferable, however, to have the medium in this space replenishable from an outside reservoir (not shown) of the medium.

In respect to electrical connections, a voltage source same'referen ce potential for both; the rod electrodes and the coating.

The rod electrodes 17a-17e are adapted to act as sensing electrodes by virtue of an interconnection thereof wherein an electric energy source 30 has one end conhected to the electrode 17a, and its other end connected to all of the'other electrodes 17b-17e. The sour'ce 30 may be a D.C. source whose voltage is less than the ionizing voltage for medium 21. For example, source 30 may provide a 410 volt output when the ionizing voltage for the medium is 6075 volts. Source 30 may also be an A.C. source whose peak voltage is less than the ionizing voltage value for the medium and whose frequency is substantially higher than the frequency of the operations which the described embodiment is called iipon to perform. a .A plurality of current responsive indicator means are trodes 17a-17c so as to connect these electrodes bye plasma path. Other light patterns will produce a plasma path exclusively between, say, electrodes 17a and 17c, or between, say, electrodes 17a, 17c and 17e.

Ordinarily the medium 21 offers a high impedance to flow of current between the electro'de 17a and any one or more of the electrodes 1712-172. When, however, a plasma path is created between electrode 17a and any one of the other electrodes this plasma path acts as alow impedance path for current flow between the two electrodes, and this current flow will take place despite the fact that the voltage between the two sensing electrodes may be considerably less than vthe ionizing respectively interposed in circuit between the electrodes MIL-17a and the source 30. In Fig. 4, these current responsive indicator means are shown as the ammeters 31b.-31e. It 'will be appreciated, however, that relays or other current responsive devices could be substituted for the shown ammeters. V The described embodiment operates in the following manner. A pattern formed by visible light is projected byan optical system (not shown) towards the glass plate 10. This pattern may, for example, have a configuration whose outline is represented by the outline of the stippled area 35 of Fig. 1. The light in this pattern penetrates the glass plate 10 and the transparent electroconductive coating 11'to enter the ionizable medium 21.

The light passing through plate 1 0.and coating 11 will initially produce an ionized condition of the medium 21 within the bounds of the pattern formed by the light. In an ordinary ionization chamber, this ionized condition would almost immediately spread throughout the whole space occupied by the medium between the electrodes 11 and 16. The presently disclosed embodiment is, however,

constructed in accordance withthe teachings of Kurt S. Lion (in his article Electronic Photography in the December l953 issue of Research Reviews published by the Office of Naval Research, Department of the Navy, Washington, D.C.), who has found that with a suitable spacing between and a suitable voltage applied between a pair of opposing electrodes in a suitable ionizing medium, it is possible to initiate an ion discharge in .the medium at a given point in a plane parallel to the electrode faces, and to have this ion discharge remainf substantially localized at its point of initiation rather spreading out through an area of the plane which is coextensive with the electrode face areas. 'In general,

.the transverse area occupied by any such ion discharge initiated at a point is of the same order as the longituldinal spacing between the electrodes. While it is not entirely necessary to use a quencher in the medium, it has been found that the transverse area occupied by a localized ion discharge can be reduced if such quencher is used, and if the voltage applied between the electrodes is adjusted to a value which produces self-quenchingof theion discharge. This advantage of a reduced transverse area by self-quenching may be obtained in what is apparenting a continuously subsisting localizedion discharge by continuously renewing the self-quenching discharge at the point of initiation with radiation :which falls on the point of initiation throughout a time period which is as long as desi ed.

From what has been said, it will be seen that the light pattern entering medium 21 will ionize this medium in a localized plasma region 35 (Figs. 1 and 2) whose outline corresponds to a close approximation to the outline of the light pattern itself. Different light patterns will produce difierent plasmaregions within the medium voltage for the medium 21. Thus, the plasma region 35 (Figs. 1 and 2) which straddles the electrodes 17a and 17b provides a low impedance path between these electrodes such that the voltage developed across these elec trodes by voltage source30 will cause a substantial current flow tlnough the plasma region 35'and through both of'these electrodes. This substantial current flow causes a marked indication to appear on ammeter 31b in circuit with the electrodes 17a and 17b. None of the otherammeters will, in this instance, produce any substantial indication inasmuch as none of the other electrodes 17c-17e are connected tothe electrode 171: through a plasma path.

From what has been said, it will be seen that differently shaped plasma regions induced by (and duplicating) differently shaped radiation patterns incident on the described embodiment will be indicated by difierent combinations of readings of the ammeters 31b-31e. For example, any one of these ammeters may give a reading while the other ammeters are absent a reading. Also, any two of the ammeters may give a reading while the other two ammeters are absent a reading. Also, any three of the ammeters may give a reading while the remaining ammeter is absent a reading, or all four ammeters may give a reading. It is thus possible with the presently describedembodimcnt to obtain'different com binations of electrical indications which separately identify' 15 ditferent radiation patterns. It will move'over be evident that, by utilizing additional voltage sources 30 connectedito urge current flow among any two of the electrodes. '17b-17e, by utilizing additional current responsive indicator means to indicate each such current flow, and by taking proper precautions to assure that each current between a given two sensing electrodes operatesone and only one indicator means, it is possible to identify many more radiation patterns than the 15 just mentioned.

In view of the modeof operation of the above-described embodiment, the .purpose of certain features thereof will be more apparent. For example, the rod electrodes 17a-17a extend no further than the outer surface of coating 16 in order to avoid favored locations of ion'discharge because of shorter ionization gaps between coating 11 and the rod electrodes than between the coat ing 11 and coating 16. Also, voids are left in coating 16in localized areas thereof surrounding the rod electrodes in order to increase the impedance between each of electrodes 17b-17e and electrode 17a in the absence of a plasma bridge connecting the last-named electrode 21. Forexample, the plasma region 35 shown in Figs; I

1 and 2 surrounds and connects the sensing electrodes 17a, 17b, butdoes not surround the other sensing ele'cs with one or more of the first-named electrodes. Also, the source 30 providesa voltage of less than the ionizing voltage. value .for medium 21 in order to prevent ionization of themedium by the voltage between the rod electrodes rather than by the voltage between the electrodes represented by coatings 11 and 16.

The above-described embodiment being exemplary only, it will be understood that the invention herein comprehends inventions differing in form or detail from the above-described embodiment. Accordingly, the invention is not to be considered as limited save as is consonant with the scope of the following claims.

f, 1;; Radiation, pattern iden fy us apparatus comprising, a first electrode of sizable extent in two coordinate directions, said electrode being pervious to ionizing radiation, an insulating member coextensive with said first electrode in said two directions and spaced therefrom in the third coordinate direction inan amount substantially less than the extent of said electrodes in either of said two coordinate directions, a coating of high impedance electroconductive material in the nature of. a second electrode deposited on the face of said member towards said first electrode; said coating being void of such -material in localized areas respectively surrounding a plurality of at least three points distributively spaced over said member to form a network of plasma sensing points, closure means to maintain an ionizable medium in the space between said electrodes,- an-ionizing'volb age source coupled between said electrodes to render said medium ionizable in a localized plasmapattern by and in accordance with a pattern of ionizing radiation which penetrates said first electrode,.a plurality of sensing electrodes in the form of low impedance rods respectively located in said two coordinate directions at said sensing points and extending through said second electrode towards said first electrode to terminate'atia distance from said first electrode which at the least is equal to the distance therefrom of said second electrode, a plurality of high impedance paths respectively connecting said sensing electrodes to said second electrode to establish the potential of the latter as the reference po tential fortthe former, electric energy source means for energizing said sensing electrodes to produce substantial current flow at less than ionizing voltage for said medium through the ones of said sensing electrodes in contactwith the plasma of a plasma pattern produced in said medium, and means to indicate which sensing electrodes have current flowing therethrough.

2. Radiation pattern identifying apparatus comprising, afirst electrode of sizeable extent in two coordinate directions, said electrode being pervious to ionizing radiation, an insulating member coextensive with said first electrode in said two directions and-spaced therefromin the third coordinate d rection in an amount substantially less than the extent of said electrodes in either of said two coordinate directions, a coating of high impedance electroconductive material in the nature of a second electrode deposited on the face of said-member towards said first electrode, said coating being void of such material .in localized areas respectively surrounding a plurality of at least three points distributively spaced over said member to form a network of--plasrna sensing points, closure means to maintain an-ionizable medium in the space between said electrodes, an ionizing voltage source coupled between said electrodes to render said medium ionizable in a localized plasma pattern by and in accordance with a pattern of ionizing radiation which penetrates said first electrode, a plurality of sensing electrodes in the form of low impedance rods respectively located in said two coordinate directions at said sensing points and extending through said second electrode towards said first electrode to terminate at a distance from said first electrode which at theleast is equal to the distance therefrom of said second electrode, a plurality of high impedance paths respectively connecting said sensing electrodes to said second electrode to establish the potential of the latter as the reference potential for the former, a source of voltage of less than the ionizing value for said medium connected by one terminal to one of said sensing electrodes and by the other terminal to the others of said sensing electrodes, and a plurality of current responsive indicator means respectively interposed between said source and said other electrodes to indicate which thereof have current flowing therethrough.

3. Radiation pattern identifying apparatus comprising,

first electrode means of sizeable extent in two coordinate directions and providing a discharge area-oft continuous extent between opposite outside bounds of said area, said first electrode means being of thinner extent in-v the third coordinate direction than either dimension of said area, and being subject in said discharge area to penetration by, ionizing radiation, second electrode means spaced from said first electrode means in the third coordinate direction by an extent less than either dimension of said discharge area of said first electrode means said'second electrode means having a discharge area coextensive with that of said first, electrode means, an ionizable medium disposed in the space between said discharge areas and adapted to be ionized in a. localized plasma pattern by and as a replica of a pattern of said penetrating, ionizing radiation to thereby sustain .an electrical discharge between the discharge areas .of said first and second electrode means, and a plurality of atc'leastthree sensing electrodes electrically insulated from. eachof first and second electrode means and respectively disposedin said medium at points which are distributively spacedin said two coordinate directions to form a network of plasma,

sensing points, said network extending inboth of said two directions, and the points thereof being separated by straight line intervals. lying within the bounds in said two directions of said discharge areas;

4. Radiation patternvidentifying apparatus comprising, first electrode means of sizeable extent in two coordinate directions and providing a discharge area of continuous extent between opposite outside bounds of said area, said first electrode means being of thinner extent in the third coordinate direction than eithertdimension of said area, and being subject in said discharge area to penetration by ionizing radiation, second electrode means spaced from said first electrode means in the third coordinate direction by an extent less than either dimension of said discharge area of said first electrode means, said second electrode means having a discharge area coextensive with that of said first electrode means, an ionizable medium disposed in the space between said discharge areas and adapted to be ionized in a localized plasma pattern by and as a replica of a pattern of said pentrating ionizing radiation to thereby sustain an electrical discharge 'be tween the discharge areas of said first and second electrode means, and a plurality of at least three sensing electrodes in the fonn of rods electrically insulated from each of said first and second electrode means and extending through said second electrode means at respective points which are distributively spaced in said two coordinate directions to form a network of plasma sensing points, said network extending in both of said twodirections, and the points thereof being separated by straight lineintervals lying within the bounds in said two directions of said discharge areas, said sensing electrodes terminating at a distance from said first electrode means which-at the least is equal to the distance therefrom of said first electrode means.

5. Apparatus as in claim 4 wherein said sensing electrodes are electrically insulated from said second elec trode means by voids formed in said second electrode means in the localized regions thereof which respectively surround said sensing electrodes. t

6. Radiation pattern identifying apparatus comprising, first electrode means of sizeable extent in two coordinate directions and providing a discharge area of continuous extent between opposite outside bounds of said area, said first electrode means being of thinner extent in the third coordinate direction than either dimension of said, area, and being subject in said discharge area to penetration by ionizing radiation, second electrode means spaced from said first electrode means in the third coordinate direction by an extent less than either dimension of said discharge area of said first electrode means, said'second electrode emanate 'vvithin' the bounds in said two directions of said discharge areas, electrical energy source means connected with said sensingelectrodes toproduce substantial current fiow at less than ionizing voltage for said medium betweenones of said sensingelectrodes in'contact with the plasma of aplasma pattern produced in said medium, and means to indicatelwhichi sensing electrodes have current flowing therethroug'h; r Y 7 f 7 7. Radiation pattern identifying apparatus comprising,

I first e'lectrode'meansof sizeable extent in two coordinate directionstand providing a discharge area of continuous extent between opposite outside bounds of said area, said first electrode means'being of thinner extent in the third coordinate direction: than either dimension of said area, and being subject in'said discharge area to penetration by ionizing'radiation, second electrode means spaced from said first electrode means in the third coordinate direction by aniextent less than either dimension of said discharge area of :said first electrode lmeans, .said second electrode meanslhavingadischarge area, coextensive with thatof saidtfirst electrode means; an ionizable medium disposed in the'space between said discharge areas and adapted to beiionized in' a localized plasmatpattern by and as a replica of a pattern ofsaid penetrating ionizing radiation to thereby, sustain an electrical discharge between the discharge areas: of-iisaid first and second electrode means a.:.v'oltage source coupled between said first and second electrode means to produce said discharge when said medium becomes ionized, a plurality of at least three sensing electrodes electrically insulated from each of first and sec- Qnd; l6Ct 1:Ode means andrespectively disposed in said medium at points which are distributively spaced in said two coordinate directions to form a network of plasma sensing points, said network extending in both of said two directions-andthe points thereof being separated by straight line intervals lying within the bounds in said two directions of said discharge areas, electrical energy source meansconnected with said sensing electrodes to produce'substantial current flow at less than ionizing voltag for said-medium-between ones of said sensing electrodes in contact with the plasma of a plasma pattern l v 8 produced in said medium,rneans to indicate which sensing electrodes have current fiov'ving-tlierethrou'gh, and a high impedance path electrically connecting said voltage source andsaid electrical energy source means. i 1

8. Radiation pattern identifying apparatus comprising, first electrode meansof sizable extent in two coordinate directions and providing a' discharge area of continuous extent between opposite outsidebounds of said area, said first electrode means being in the formof a'transparent electroconductive conducting on a transparent insulating substrate member, whereby said first electrode means is of thinner extent in the third coordinate direction than either dimension of said 'area and is 'subjectin said discharge area to penetration by ionizing radiation, second electrode means spaced from said firsttelectrode means in the third coordinate direction by an extent less than either dimenision'of said discharge area of said first electrode means said second electrode means having adischarge area coextensive with that' of first electrode means, and saidsec'ond electrode means being in the form of an electroconductive coating on an insulating base member, anionizable medium disposed in the space between said discharge areas and adapted to be ionizedin a localized plasma pattern by .and as a replica of a pattern of said penetrating ionizing radiation .to thereby sustain an electrical discharge between the discharge areas of said first and second electrode means, and a plurality of at least three sensing electrodes in the form of rods electrically insulated from each of, said first and second electrode means and extending through said base memberand second elec-' trode means at respective points which are distributivcly spaced in said two coordinate directions to form a network of plasma sensing points, said network extending in both of said two directions, and the points thereof being separated by straight line intervals lying within the bounds in said'two'directions of said discharge areas, said sensing electrodes terminating at a distance from said first electrode means which atrthe least is equal to the distancev therefrom of said first electrode means, and said sensing electrodes being insulated from said first electrode means' by voids formed in said second electrode means in the respective localized areas thereof surrounding said sensing electrodes.

References Cited in'the file of this paten UNITED STATES PATENTS Nuefeld July v22, 1952 2,609,419 Blair Sept. 2, 1952 2,618,697- Metcalf' Nov; 18, 1952 2,1642 ,548 Wallace June 16, 1953 '2,763,789 Ohmart Sept. 19, 1956 2,764,695 -Sept. 25, 1956 Porter et al. 

